1. Field
The present disclosure relates to a high electron mobility transistor, and/or more particularly to a high electron mobility transistor having a normally-off characteristic.
2. Description of Related Art
A nitride semiconductor device may be used as a power device for power control. In a power conversion system, an efficiency of the power device may affect the efficiency of the entire system. Examples of power devices include a metal-oxide-semiconductor field-effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT), which are based on silicon (Si). However, increasing the efficiency of Si-based power devices may be limited by Si properties and/or manufacturing processes. Other examples of power device include power devices using a III-V group-based compound semiconductor, such as a high electron mobility transistor (HEMT). The HEMT may include a heterojunction structure of a compound semiconductor.
HEMTs may include semiconductor layers having different electrical polarization characteristics, wherein one semiconductor layer having a relatively high polarizability may induce a 2-dimensional electron gas (2DEG) in the other semiconductor layer. Since the 2DEG may be used as a channel, the HEMT may have a high electron mobility. Also, HEMTs may include a compound semiconductor having a wide band gap. Thus, a breakdown voltage of the HEMT may be higher than that of a general transistor. The breakdown voltage of the HEMT may increase in proportion to a thickness of a compound semiconductor layer including 2DEG, for example, a gallium nitride (GaN) layer. Also, a normally-off function may be desired for a normal operation of the power device.